How to calculate a staircase: risers, treads and slope

Updated October 10, 2026

A comfortable staircase is mostly arithmetic: a whole number of equal risers that add up to the height to climb, and a tread deep enough for a natural pace. Here is the method, then an example you can check in the calculator.

1. Measure the height to climb

Measure from the finished floor below to the finished floor above, not from the structure. Floor coverings that are not laid yet change the height by a few centimetres, so measure with them in mind.

2. Choose the number of risers

Divide the height by the riser height you want (often 16 to 18 cm) and round to the nearest whole number. The real riser is then the height divided by that number: all risers are equal.

Uneven risers are a classic cause of trips: never mix heights on a flight.
The number of treads is one fewer than the number of risers when the top landing counts as a step.

3. Deduce the tread with Blondel’s rule

Blondel’s rule links comfort to the length of a pace: 2 × riser + tread ≈ 63 cm (between 60 and 65 cm). Once the riser is known, tread = 63 − 2 × riser.

Worked example: 270 cm to climb

270 ÷ 17.5 = 15.4, so 15 risers of 270 ÷ 15 = 18.00 cm. Tread = 63 − 36 = 27 cm.

14 treads of 27 cm: horizontal run of 378 cm.
Slope: about 33.7°.
Stringer length: about 4.65 m.
For a 90 cm wide stair, about 3.4 m² of tread surface to buy in wood.

What this does not cover

Building regulations set limits on riser, tread, headroom, handrails and landings, and they differ by country and building type. The structure of the staircase (slab, stringers, supports) must be designed separately. The calculator gives a preliminary layout, not a validation or an execution drawing.

To price the work, the labour cost calculator turns hours and wages into a cost per unit.

General information, checked at the date shown. It does not replace advice from a professional for your situation.

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